Question

I saw this in someone’s code and thought wow, that’s an elegant way to solve this particular problem, but it probably violates good OO principles in an epic way.

In the constructor for a set of classes that are all derived from a common base class, he requires a reference to the instancing class to be passed. For example,
Foo Foo_i = new(this);

Then later on Foo would call methods in the instancing class to get information about itself and the other objects contained by the instancing class.

On the one hand, this simplifies a TON of code that models a 5-layer tree structure in hardware (agents plugged into ports on multiple switches, etc). On the other hand, these objects are pretty tightly coupled to each other in a way that seems pretty wrong, but I don’t know enough about OOA&D to put my finger on it.

So, is this okay? Or is this the OO equivalent to a goto statement?

Answer 1

I try and avoid this if I can just from an information hiding point of view. The less information a class has or needs the easier it is to test and verify. That being said, it does lead to more elegant solutions in some cases so if not doing it is horribly convoluted involving an awful lot of parameter passing then by all means go for it.

Java for example uses this a lot with inner classes:

public class Outer {
  private class Inner {
    public Inner() {
      // has access to the members of Outer for the instance that instantiated it
    }
  }
}